Hi Alex,
On Jul 16, 2010, at 2:02 AM, Alexandru Csete wrote:
> I suggest you leave the pre-demodulator settings as they are in the
> example and add a rational resampler after the demodulator, see
> examples/audio/test_resampler.py on how to use it.
I looked at the rational resample example, and modified the usrp2_wfm_rcv.py
script. The results weren't good, and it appeared that the playback was
re-sampled to a lower rate, with the music playing back as if the speed was
slowed down.
The audio_rate, when computed is 32051Hz, but using that value completely hangs
the system.
When I hard-code the value to 32050Hz, the system plays back, but at a slower
speed.
The output sample rate is set to 48000Hz.
I have attached the patch below, could you let me know if the modifications are
correct?
Elvis Dowsn
diff --git a/gnuradio-examples/python/usrp2/usrp2_wfm_rcv.py
b/gnuradio-examples/python/usrp2/usrp2_wfm_rcv.py
index 1783660..0184725 100755
--- a/gnuradio-examples/python/usrp2/usrp2_wfm_rcv.py
+++ b/gnuradio-examples/python/usrp2/usrp2_wfm_rcv.py
@@ -51,7 +51,10 @@ class wfm_rx_block (stdgui2.std_top_block):
help="set volume (default is midpoint)")
parser.add_option("-O", "--audio-output", type="string", default="",
help="pcm device name. E.g., hw:0,0 or surround51
or /dev/dsp")
-
+ parser.add_option("-i", "--input-rate", type="eng_float",
default=32050,
+ help="set input sample rate to RATE (%default)")
+ parser.add_option("-o", "--output-rate", type="eng_float",
default=48000,
+ help="set output sample rate to RATE (%default)")
(options, args) = parser.parse_args()
if len(args) != 0:
parser.print_help()
@@ -66,6 +69,7 @@ class wfm_rx_block (stdgui2.std_top_block):
# build graph
+ # USRP2 source
self.u = usrp2.source_32fc(options.interface, options.mac_addr)
adc_rate = self.u.adc_rate() # 100 MS/s
@@ -76,6 +80,7 @@ class wfm_rx_block (stdgui2.std_top_block):
demod_rate = usrp_rate / chanfilt_decim
audio_decimation = 10
audio_rate = demod_rate / audio_decimation # ~32 kHz
+ print "audio rate =", audio_rate
#FIXME: need named constants and text descriptions available to
(gr-)usrp2 even
#when usrp(1) module is not built. A usrp_common module, perhaps?
@@ -87,11 +92,13 @@ class wfm_rx_block (stdgui2.std_top_block):
dbid == 0x0040 or #usrp_dbid.TV_RX_REV_3
dbid == 0x0043 or #usrp_dbid.TV_RX_MIMO
dbid == 0x0044 or #usrp_dbid.TV_RX_REV_2_MIMO
- dbid == 0x0045 ): #usrp_dbid.TV_RX_REV_3_MIMO
+ dbid == 0x0045 or #usrp_dbid.TV_RX_REV_3_MIMO
+ dbid == 0x0053 ): #usrp_dbid.WBX
print "This daughterboard does not cover the required frequency
range"
print "for this application. Please use a BasicRX or TVRX
daughterboard."
raw_input("Press ENTER to continue anyway, or Ctrl-C to exit.")
+ # channel filter co-efficients
chan_filt_coeffs = optfir.low_pass (1, # gain
usrp_rate, # sampling rate
80e3, # passband cutoff
@@ -101,8 +108,22 @@ class wfm_rx_block (stdgui2.std_top_block):
#print len(chan_filt_coeffs)
chan_filt = gr.fir_filter_ccf (chanfilt_decim, chan_filt_coeffs)
+ # wide-band FM demodulator
self.guts = blks2.wfm_rcv (demod_rate, audio_decimation)
+ # rational resampler
+ input_rate = int(options.input_rate) # 32050 Hz default
+ #input_rate = audio_rate # 32051 Hz as computed
earlier (line 82), but hangs the application
+ output_rate = int(options.output_rate) # 48 kHz default
+
+ interp = gru.lcm(input_rate, output_rate) / input_rate
+ decim = gru.lcm(input_rate, output_rate) / output_rate
+
+ print "interp =", interp
+ print "decim =", decim
+ rr = blks2.rational_resampler_fff(interp, decim)
+
+ # volume control
self.volume_control = gr.multiply_const_ff(self.vol)
# sound card as final sink
@@ -111,7 +132,7 @@ class wfm_rx_block (stdgui2.std_top_block):
False) # ok_to_block
# now wire it all together
- self.connect (self.u, chan_filt, self.guts, self.volume_control,
audio_sink)
+ self.connect (self.u, chan_filt, self.guts, rr, self.volume_control,
audio_sink)
self._build_gui(vbox, usrp_rate, demod_rate, audio_rate)
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